Analysis is the process of converting text, like the body of any email, into
tokens or terms which are added to the inverted index for searching.
Analysis is performed by an analyzer which can be
either a built-in analyzer or a custom analyzer
defined per index.

This same analysis process is applied to the query string at search time in
full text queries like the
match query
to convert the text in the query string into terms of the same form as those
that are stored in the inverted index.

For instance, a user might search for:

"a quick fox"

which would be analysed by the same english analyzer into the following terms:

[ quick, fox ]

Even though the exact words used in the query string don’t appear in the
original text (quick vs QUICK, fox vs foxes), because we have applied
the same analyzer to both the text and the query string, the terms from the
query string exactly match the terms from the text in the inverted index,
which means that this query would match our example document.